Remove deprecated function ioutil.ReadDir

What does this MR do?

This MR removes usage of deprecated ioutil function; ReadDir as suggested by the documentation

This is my first MR, therefore any comments about workflow would be appreciated and gladly accepted :)

What are the relevant issue numbers?

N/A

Does this MR meet the acceptance criteria?

• [-] Changelog entry added
• Documentation created/updated for GitLab EE, if necessary
• Documentation created/updated for this project, if necessary
• Documentation reviewed by technical writer or follow-up review issue created
• Tests added for this feature/bug
• Job definition updated, if necessary
  • Auto-DevOps template
  • Job definition example
  • CI Templates
• Conforms to the code review guidelines
• Conforms to the Go guidelines
• Security reports checked/validated by reviewer